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  Forum Index - Guides - Electronics Guide Part 1 - the Basics
Author Initial Thread

Joined: Nov 11, 2007
Posts: 120
Post Subject: Electronics Guide Part 1 - the Basics
Posted on: May 26, 2008


Electricity is brilliant stuff. Without it the world would be a very different place. A bleak civilisation with no computers, Internet access or pop-up toasters. A place where even FusionMods wouldn't even exist - unthinkable. Despite this, very few people know what electricity actually is let alone how to use it. Most people's electronic knowledge extends to knowing that when you hit that white thing on the wall, the room lights up. This is a shame, especially for modders, since with just the very basics of electronics under your belt you can accomplish some pretty impressive things which will make your case stand out amongst the best of 'em.

In this series of guides I'm going to be taking you through the world of electromodding. In Part One we'll look at the theory behind electricity or components and then in the next I'll take you through building a neat device for your rig that uses this theory practically. In this, the first instalment, we'll be looking at the very basics � What is electricity? And more importantly, How do you go about using it?


If you've ever picked up a book or read an article on Electronics you'll know that there are plenty of analogies to try and explain everything about electricity in a few seconds. Pressurised water pipes, rivers, roads full of traffic, the list goes on. But because electricity is such a weird thing, it doesn't behave like things you experience in day to day life. Because of this, I always think it's best to get a bit geeky and look at what electricity actually is.

Anyone who has experienced the pure unadulterated joy of having to attend science classes will know that everything is made of little bits called atoms. A part of an atom is an electron and in some materials, like metal, atoms can have a few of these spare. These 'free electrons' can move around the metal when forced, this is electricity.

The term "electricity" is far too general though: so general that I believe it better to use more specific terms. Electricity has three main parts: Voltage, Current and Resistance; these are what we'll be talking about instead. Let's take a look at each of them.

Current: This is the flow of those little electrons. Just like distance is measured in centimetres or inches, Current is measured in Amps; the more electrons that pass through a wire or component per second, the greater the current. One Amp of current is approximately 6,240,000,000,000,000,000 electrons per second.

Voltage: (aka Potential Difference) Imagine a metal wire as a piece of pipe, and the free electrons in it as little styrofoam balls. If you held this pipe perfectly flat, how would you make the balls start to flow? You'd have to raise one side of the pipe up or down relative to the other side. In other words you'd have to make a difference in height (potential) at either end. This is what voltage is all about, and is what makes the electrons move. In other words, voltage is the "pushing" force which moves the current. Current doesn't exist without voltage. Voltage is measured in, you guessed it, Volts, named after the Italian Count, Alessandro Volta.

Resistance: Resistance is simply anything that hinders the flow of current. Everything, even wire, has some resistance, and it is measured in Ohms, named after the 19th Century German physicist, Georg Simon Ohm, after whom the cornerstone Law is named (see below). Without resistance there would be no voltage. Every electrical conductor has some resistance, even a "short circuit". If a piece of wire had truly no resistance then the voltage or potential difference across it would be "shorted out" making the votage = 0. As stated above no voltage = no current.

All these things are linked together by the most common formula in electronics, Ohm's Law (where V is voltage, I is current and R is resistance):

V=IR thus I=V/R thus R=V/I

...this looks scarey at first but it is much simpler than it looks. What it means is that if you take the current through a component and multiply it by the resistance of that component you'll be able to figure out the voltage. That if you divide the voltage across a component by the resistance of the component you'll get the current. And that if you divide the voltage across a component by the current through it you'll get the resistance. That might not sound that useful, but we'll be needing that simple equation quite a bit as you'll see later. If you draw a triangle with voltage at the top and current and resistance on the bottom you can easily work out each of these equations.. simply cover up what you want to find and it will show you the sum. Magic.

Remember Voltage is ACROSS a component and Current flows THROUGH a component. This is a vital concept to understand.

Types of Circuit

There are three main methods you can connect two or more components together to form a circuit: a circuit is just an electrical loop that the current can flow around, thus performing useful tasks like drive fans and light-up LEDs. These three methods are called series, parallel and mixed. Let's take a look...


Components are connected to the circuit sequentially, or one after the other. The current flowing through the components is the same everywhere but the voltage can be different for each components.


As the name would suggest, components are connected on separate paths, allowing current to flow through both simultaneously. In this arrangement, voltage is always the same but current can be different for each component.

This is just a mixture of the above two. To figure out what's happening with the voltage and current in this one you have to split it into series and parallel sub-sections and look at each one. We'll look at this more when we come across a mixed circuit.

The Molex Connector

Molex connectors are the electromodder's best friend. They provide stable, accurate power on tap wherever you need it inside, or even a little outside your case. If you're reading this you'll probably have pushed in and pulled out a good few molex connectors in your time, yet most people don't know what those 4 wires are. All that you need to know about a molex is what voltage each of the lines are, take a look at this diagram:

You may wonder why there are two 0V lines, surely one is enough, right? Well, one 0V line is enough for our purposes since every circuit will share this common 0V connection. The complex circuits inside things like hard-drives are a different matter though, providing different 'routes' to 0V can help keep interference low and power more stable when it comes to high frequency signals. We'll look more into the weird effects of high frequencies and inductance when we come onto building a pulse width modulator for controlling fans with in later parts. For now though, forget I said anything.

The First Project

Components are the building blocks of every circuit. We connect them together with wires or copper tracks to make circuits, but it's the components that do all the work. The first thing we're going to be making in this series is a simple LED light for your case which will use two of the most common components. This will take us through what a resistor does, what an LED does, how to calculate resistor values and how to read circuit diagrams... oh, and you'll get a pretty light at the end. What more could you want?

I'm pretty sure you'll have come across LEDs before: the average modders case probably has about a dozen of the things; many of you will also know that LED stands for Light Emitting Diode. They come in all shapes, size and colours, if you buy them fresh they might look something like this...

You may have noticed that one leg is shorter than the other and, if your eyes are good, that there is a flat-side to the base of the LEDs body. Being a Diode (albeit one that produced purty colours!), and LED will only permit current to flow in one direction. You might have discovered this when building your PC: basic stuff like your reset button (and elementary push-to-make switch) can be connected either way around, but your Power LED & Hard Drive LED will only light up when the positive and negative terminals are correctly matched.

This is why the legs are different lengths: the positive leg is always the longer of the two. If you connect an LED the wrong way round it won't kill it - it just wont produce any light.

So, from what we know about LEDs and molex connectors gives us this circuit diagram. The direction of the LED is indicated by the direction of the triangle, the negative short leg is always the point of the triangle:

Unfortunately it's not as easy as that, and that circuit diagram is a recipe for LED death. This is because LEDs have maximum 'forward voltage' limits (usually between 1.8V and 3.6V) and maximum current limits (usually between 10mA and 35mA). To take some of the voltage and limit the current to protect the LED we need to use a component called a resistor, which look like this:

The resistor will absorb some of the voltage across it when we place it in series with the resistor. The amount of voltage it takes depends on how big it's resistance is which is measured in Ohms. To work out this value we need to use a formula derived from ohms law which looks like this:

Scary, huh? Let's do an example using these LED specs:

LED Forward Voltage: 2.2V
LED Max Current: 25mA
Power Supply: 5V Molex

So, using that formula we'll take the LED Forward Voltage away from the Power Supply to give 5�2.2 = 2.8V. This is the voltage the resistor needs to take across it. Now we need to divide this by the Max Current � this is where most new comers go wrong. The formula expects the current to be in amps, but we've been given the current rating in milliamps. Now, 1 milliamp is one thousandth of an amp, so to convert from mA to A we need to divide by 1000. This gives us a value of 25/1000 = 0.025A. We can now divide 2.8/0.025 to give us the value of resistor needed! The answer is, drum roll please, 112Ohms. We can't actually use this value for reasons I'll go into in the next part when we'll be covering the practical implementation of the circuit in our rig but we'll pretend we can for now. Our final circuit diagram now looks like this:

If you were to use this circuit, your LED is ensured a bright and happy life. This is the diagram we'll be using in the next part of the guide to construct our case light.


That's all for this part folks. In the next part of the series we'll be using the circuit diagram we just worked out to make a working LED light for our case, looking at the practical side of the theory we've covered. If not all of what I've covered is sticking in your brain, don't worry about it. Electronics is far easier to learn by doing than by reading up on equations and diagrams. As the series progresses you should find yourself getting more of a 'feel' for it and getting confident enough to tackle more complex circuits.

Thanks For Reading Take It Easy Sincerly Ryan Armstrong

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Dayton Metro PC Owner

Joined: Jul 24, 2007
Posts: 1235
Post Subject: subject
Posted on: May 26, 2008

I love your work. Well done. For someone like myself, who took Electronics Engineering for 1 semester, this is a welcome refresher. I remember most of what you have covered here, but I am REALLY looking forward to the later parts of this guide.

Core2 Quad Extreme QX96500-ES @ 3Ghz, 4gb Patriot DDR2-1066Mhz RAM, 4gb Intel Turbo Memory, 3x 500GB WD Blue drives, Samsung DVD-RW, GTX 560ti-1gb Gfx card.
Future Mods: none for Freshwater. Next build will be all new.
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Selfmade Modder

Joined: Jun 30, 2006
Posts: 4540
Post Subject: subject
Posted on: May 28, 2008

great guide. Dealing with electricity has always been my hardest part to modding. I never remember all the stuff and it drives me crazy. I have an uncle who's an electrician and I'm regularly talking with him over what he's gotta think is some incredibly basic stuff, lol

If con is the opposite of pro, is Congress the opposite of progress?
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